Boyd and Richerson (1985) start with the observation that evolution has only recently made contributions to the social sciences. According to the authors, the most important reason is that evolution has not had much to say about culture.
The goal of the book is to outline an evolutionary theory of cultural organisms. Culture is defined as “...the transmission from one generation to the next, via teaching, and imitation, of knowledge, values, and other factors that influence behavior” (2). Moreover, transmission occurs via structures or “...patterns of socialization by which a given trait or set of traits are transmitted in a given society (2). One example of a structure is peer to peer enculturation. A theory of cultural evolution should do two things. First, it should be able to predict the effects of structures in a culture. Second, the theory should also explain how different structures evolve.
In order to satisfy these conditions, the authors develop mathematical models. The mathematical models are borrowed from genetics and informed by empirical studies. The resulting models form their “dual inheritance theory.” Boyd and Richerson’s goal in the book is not to provide the correct theory of human evolution. Their aims are to “...clarify the logical relationships between cultural transmission and other Darwinian processes and stimulate social scientists…” (2).
An Informal Sketch of the Dual Inheritance Model
Here the authors explain their basic argument and some implications for social science. They start with the observation that in biology, there is a shared consensus on how genetic inheritance works and how forces of evolution (natural selection, recombination, mutation, and drift) relate to changes in genetics and phenotypes. The goal would be for cultural evolutionary theory to reach something like this level of theoretical success. Boyd and Richerson borrow mathematical models from genetics to employ in their theory.
Diagram from Boyd and Richerson, page 5
Environment, Learning, and Culture
The core idea behind biological evolution is that certain characteristics are genetically inherited. The genotypes inherited in part determine the phenotypes or behavioral-observable characteristics of the organism. The concept of phenotypic adaptation refers to an organism’s ability to adapt its behavior to the environment. For example, bacteria synthesize certain enzymes only under certain environmental conditions. Plants change their phenotypes depending on the environment. Via learning, humans too change their behavior. The question arises, is culture more like phenotypic adaptation or more like a genotype, which is inherited? Boyd and Richerson hold that the difference is that behaviors acquired via phenotypic adaptation end when the organism dies. By contrast, cultural behaviors are passed on. This suggests that culture is inherited and in this way is like a genotype. Since culture is inherited, the properties of the population are influenced by culture. So, culture has population level consequences.
The authors are making a sharp distinction between genotype and phenotype, environment and culture, and social learning. Cultural traits are thought as genotypes that are inherited, and they affect one’s phenotypes or one’s behavior. Social learning is the means of transmission.
The Structural Properties of Human Cultural Inheritance
As mentioned above, structures are understood as patterns of inheritance. Cultural structures are significantly different from how inheritance occurs in genetics. One difference is that in culture, inheritance is more complex: from parents, peers, and others. Another difference is that cultural inheritance occurs over time. A third difference is that cultural traits can be Lamarckian in kind; traits are acquired via use.
The Forces of Cultural Evolution
The evolutionary forces included in the theory are random variation, genetic drift, and guided variation, biased transmission, and natural selection. Interestingly, the authors note that humans will use ordinary learning such as trial and error learning along with standards or tastes to guide the kinds of cultural traits that are inherited. In regards to bias transmission, two are mentioned. Direct bias occurs when one adopts a cultural trait on the basis of properties it has. It is easier to copy the practice of eating sweet foods. Another bias is frequency dependent bias. As the name suggests, it occurs when a cultural trait is adopted on the basis of how common or rare the trait is.
Lastly, we are told that if natural selection operates on cultural inheritance, then genetics and cultural behaviors can diverge. New predictions emerge. Selection no longer acts simply on genes but on cultural traits too. People may be motivated to pass on their ideas, not just their genetics.
The Human Sociobiologist View of Culture
The sociobiologist holds that human behavior aims to maximize an individual’s genetic fitness or survival. The sociobiologist thus explains social-cultural behavior in terms of fitness maximizing. Counter examples, that is, examples showing that some behaviors are not fitness maximizing, do not automatically discredit sociobiology. This is because the sociobiologist has room to explain behavior that is not fitness maximizing. Evolution is imperfect. Changes in one variant may change others. Populations may not yet be at an equilibrium. So, it seems that the best way to compete with sociobiology is to show that cultural evolution provides better hypotheses or theories than the sociobiologist.
Inheritance as a Shortcut to Individual Learning
The cultural evolutionist, unlike the sociobiologist, may hold that some behavior evolves even when it does not maximize genetic fitness. Moreover, cultural evolutionary theory holds that cultural inheritance evolves in situations where the costs of individual learning are high. Cultural inheritance can be a shortcut to these forms of individual learning, e.g., trial and error learning. Much work has to be done to understand what cultural learning is and how it evolves. Imagine a scenario where imitating others becomes a shortcut to learning. As more and more imitators enter the population, less and less people are actually tracking the environment. Eventually, imitation becomes unreliable since no one is tracking the environment. So a balance must be struck between imitation and individual learning. A good cultural evolutionary theory should inform us about these balances.
The book will be about two questions. 1. How can structural patterns of inheritance produce observed patterns of human behavior? 2. Are these structural features genetically adaptive? The authors position themselves against the sociobiologist. Nevertheless, the authors don’t take themselves to have settled the debate, or to have established the theory. They believe that their book only shows that cultural evolutionary theory is consistent and worthy of further exploration.
Chapter 2. Some Methodological Preliminaries
Boyd and Richerson adopt mathematical models to understand how cultural inheritance can influence the behavior of individuals. They think that this method may seem simplistic, reductionist, or deterministic. This chapter defends their methodology.
To understand observed biological properties, Darwin proposed that there was a system of inheritance, variation, and selective retention. Cultural evolutionary theory makes the same move. The goal is to investigate how the actions of individuals, across time, result in the patterns of cultural transmission that we see today. The hope is that it will be fruitful when directing us to ask what are the causes of cultural variation.
To understand population level phenomena, the authors employ recursion models that start with assumptions about enculturation and life history. Boyd and Richerson give the example of the domesticity trait. They factor in traits like number of children, number of parents displaying the value of domesticity, and the effects of experience. Since the goal is to predict how this trait will spread through generations, the equation is applied iteratively. Then we can see if the trait reaches some equilibrium.
Levels of Explanation
Some theorists have argued that we must explain large scale social phenomena by reference to individual psychological facts. Others have said this is backward. They start with social forces to explain the individual. The book says their model takes these levels to be reciprocally linked. Social forces influence the individual and vice versa. For example, individuals can change their phenotypes by rational calculation. Other times, social forces play a factor, say when economies support households with more children, then the cultural variants of the parents will have significant population level consequences.
Modeling Complex Phenomena
The theory requires various factors: how individuals acquire and change attitudes and beliefs as well as how these change and interact with genes or the environment. Then we have to see how these effects feedback into attitudes and beliefs. Moreover, each population will be different from the next. A general theory covering all these intricacies is perhaps too complex. Boyd and Richerson instead opt for “sample theories.” These are simple theories that focus on a few, manageable conditions. They balance simplicity with approximation. The collection of sample models form their general theory. They compare this approach to what is done in evolutionary biology. Evolutionary biologists also don’t have models that cover all the phenomena. Rather, they have various models for various processes ( selection, mutation, drift) and phenomena (sexual selection, speciation). They also have models specific to populations.
In Defense of Simple Models
Simple models are preferred over detailed models because “... (1) they [detailed models] are not useful for representing generic processes, (2) they are hard to understand, (3) they are difficult to analyze, and (4) they are often no more useful for prediction than simple models” (25).
The Utility of General Theory
A critic may say that having a general theory made up of many sample theories is loose science. Boyd and Richerson point out that their approach has benefits. A general theory links many theories together. It suggests what characteristics sample theories should have. The theory suggests that other fields should seek explanations. For example, cultural evolution suggests that social science should look for a link between the individual and large scale social phenomena.
Testing the Theory
In biology, scientists would not be surprised to find that sample theories were poor predictors. This is because the theories often abstract or idealize various real world factors. Given the complexity of the domain, this is not an embarrassment. Nevertheless, experiment is important. Science satisfies itself with a general theory suggesting that the sample theories are correct at a qualitative level.
Use of Data
Boyd and Richerson acknowledge that they have not covered all the literature and that more data needs to be collected. Their goal in drawing on data from other disciplines is to illustrate their models and show that they are reasonable.
The starting point of the book is that there is an analogy between cultural and genetic evolution. But there are important differences, and paying attention to these differences helps us understand why two different sources of inheritance evolved.
Boyd R. & Richerson P. J. (1985). Culture and the evolutionary process. University of